The invention relates to a process for the production of a stable peracetic acid product by feeding hydrogen peroxide and acetic acid continuously into an aqueous reaction medium that contains hydrogen peroxide, acetic acid, peracetic acid and an acid catalyst, in which medium the hydrogen peroxide and acetic acid react and form peracetic acid, and by distilling a peracetic acid concentrated distillate continuously from the reaction medium. The invention also relates to a stabilized peracetic acid product and a process for the stabilization of a product containing peracetic acid, water and other substances.
Peracetic acid can be used as both a bleaching chemical and a disinfection chemical. Distilled peracetic acid (dPAA), being an environment-friendly chemical, is very well suited for the bleaching of pulp. With the help of peracetic acid, the total selectivity of TCF bleaching (Total Chlorine Free) can be improved by the use of acid delignification steps between alkaline steps (Kemira patent application No. FI 974575). Besides delignification, the peracetic acid step also improves pulp brightness, for which reason it is excellently suited for the after-bleaching of both ECF and TCF pulps (Kemira patent application No. FI 990445).
The disinfectant properties of peracetic acid are exploited, for example, in the improving of the shelf life of pigment suspensions, which enables waste paste to be recycled (FI patent application 982735) in paper mills. The bleaching properties of peracetic acid can also be exploited in the bleaching of the pigment suspension used in the paper machines (FI 980417).
In the storage and transport of distilled peracetic acid, the special characteristics of the chemical must be taken into account. In order to inhibit the decomposition (H2O2xe2x86x92H2O+xc2xdO2) characteristic of peroxides, the product is stabilized in connection with its production. Regarding peracetic acid it is also to be taken into account that both its storage and its transport must take place under refrigeration. At an elevated temperature, distilled peracetic acid reverts to its initial substances, whereby a so-called equilibrium mixture of peracetic acid is formed (CH3COOOH+H2Oxe2x86x92CH3COOH+H2O2).
In cellulose mills and in the bleaching of pigments, large amounts of peracetic acid are required regardless of whether the question is of production or of full-scale trial runs. Through on-site production, storage and transport are avoided.
In connection with continuous-working production of distilled peracetic acid there always forms, as a byproduct, the medium of the peracetic acid process, the so-called bottom product (ePAAb), i.e. an equilibrium mixture; an effort is made to maintain its composition in a stationary state. During the process, small amounts of impurities also concentrate in the reaction medium, and thus this rather dilute peracetic acid solution, i.e. the bottom product of distillation (ePAAb), contains, among other things, all of the metallic impurities originating in the raw materials, primarily in acetic acid. Its storage and transport must therefore be carried out with great care.
It is generally known to prepare peracetic acid by feeding hydrogen peroxide and acetic acid continuously into an aqueous reaction medium which contains hydrogen peroxide, acetic acid, peracetic acid and an acid catalyst and in which hydrogen peroxide and acetic acid react and form peracetic acid, and by distillating a peracetic acid concentrated distillate continuously from the reaction medium (Degussa U.S. Pat. No. 3,264,346, DGS GB 949,094, FMG GB 1,014,361, Degussa EP 296 328, Eka Chemicals EP 789 016, Solvay EP 1 004 576). Both distilled peracetic acid and the said reaction medium are obtained as products.
In known processes, the bottom product, i.e. the spent reaction medium (ePAA) is mentioned only as a problematic byproduct (as an effluent).
The object of the present invention is to provide a process for the exploitation of the spent reaction medium. When a reaction medium ePAAb containing hydrogen peroxide, acetic acid, a small amount of peracetic acid and an acid catalyst is mixed as such with a peracetic acid concentrated distillate dPAA, the ePAAb+dPAA stability of the forming mixture is very poor, and its peracetic acid concentration decreases rapidly during storage. It has also been observed, unexpectedly, that even cold storage (0xc2x0 C.-10xc2x0 C.) is not alone capable of stabilizing the peracetic acid product.
The problem has now been solved by a new process for the production of a stable peracetic acid product, the process being mainly characterized in the bringing together of the distillate, the reaction medium and a substance that at least partly neutralizes the acid catalyst.
The inventive idea of the present invention is thus that the bottom product formed as a byproduct, i.e. the spent reaction medium of the distillation of peracetic acid, can be combined with the actual product. The acid catalyst arriving along with the bottom product is neutralized before the mixing. Thus the storage and transport of a dilute and less pure peracetic acid is avoided.